Cryptomator normally encrypts files stored on cloud services and relies on an integrity check of the vault configuration file. An attacker who can modify this file bypasses host authenticity validation during Hub key loading, creating a man‑in‑the‑middle scenario. The vulnerability enables a malicious endpoint to be paired with a legitimate authentication endpoint, allowing the extraction of access tokens used to communicate with the cloud. The flaw is characterized by CWE‑346, CWE‑354, CWE‑451, and CWE‑923, and has a CVSS score of 7.6, indicating high severity.

Cryptomator, the open‑source client for encrypted cloud storage, is affected. Users who run versions prior to 1.19.1 and unlock Hub‑backed vaults in environments where an attacker can alter the vault.cryptomator file are vulnerable. Version 1.19.1 contains a patch that restores integrity verification of the configuration file and the existing hosts list. The vulnerability applies to all releases before that point.

The risk is high due to the potential for token theft, but the EPSS score <1% indicates low likelihood of widespread exploitation at present. The vulnerability is not cataloged in CISA’s KEV list. Exploitation requires the attacker to have the ability to tamper with the configuration file on the client machine or the network path used to retrieve it, making it most likely in scenarios where local credentials are compromised or the user accepts malicious updates. The attack path is relatively straightforward once file tampering is possible, and it can result in unauthorized API calls to the cloud provider on the victim’s behalf.